Single wafer method and apparatus for drying semiconductor substrates using an inert gas air-knife

ABSTRACT

In one aspect, a method of drying a substrate includes (1) setting a gas delivery angle for an air knife used during an immersion-drying process; (2) using the air knife during immersion drying of a hydrophilic substrate; and (3) using the air knife during immersion drying of a hydrophobic substrate. The gas delivery angle is unchanged during immersion drying of both the hydrophilic substrate and hydrophobic substrate. Numerous other aspects are provided.

[0001] The present application claims priority from U.S. Provisional Patent Application Serial No. 60/388,277, filed Jun. 13, 2002, which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] This invention is concerned with semiconductor manufacturing and is more particularly concerned with techniques for drying a substrate.

BACKGROUND OF THE INVENTION

[0003] It is known to process a semiconductor substrate to achieve a dry and low-contamination condition after processing steps such as chemical mechanical polishing (CMP) and scrubbing. It has also been proposed to employ immersion drying to semiconductor substrates using the so-called Marangoni effect. An example of a Marangoni dryer is disclosed in co-pending, commonly-owned U.S. provisional patent application Serial No. 60/335,335, filed Nov. 2, 2001 (Attorney Docket No. 5877/L), entitled “Single Wafer Immersion Dryer and Drying Methods”, and which is hereby incorporated herein by reference in its entirety.

[0004] In Marangoni drying, a substrate is raised in a vertical orientation from a fluid bath, and an alcohol vapor is delivered to a meniscus that is formed at the substrate/fluid interface. The alcohol vapor reduces the surface tension at the meniscus, thereby creating a “Marangoni” force resulting in a downward liquid flow opposite to the substrate lift direction. As a result, the substrate surface above the meniscus is dried.

[0005] Marangoni drying is promising in terms of substrate throughput, absence of water marks, and low contamination levels achieved. However, it would be desirable to achieve comparable results without the inconveniences of delivering and exhausting hazardous alcohol vapor.

SUMMARY OF THE INVENTION

[0006] According to an aspect of the invention, a method of drying a substrate is provided. The inventive method includes raising the substrate out of a fluid bath. During the raising step, an air-knife is applied to a meniscus formed at an interface between the substrate and the surface of the bath.

[0007] As referred to herein, an air-knife is not limited to using atmospheric air, but rather may use any suitable gas, including, for example, an inert gas such as nitrogen or argon.

[0008] In another aspect of the invention, a method of drying a substrate includes (1) setting a gas delivery angle for an air knife used during an immersion-drying process; (2) using the air knife during immersion drying of a hydrophilic substrate; and (3) using the air knife during immersion drying of a hydrophobic substrate. The gas delivery angle is unchanged during immersion drying of both the hydrophilic substrate and hydrophobic substrate.

[0009] It has been found that application of an air-knife to a fluid meniscus in conjunction with substrate immersion drying produces low contamination outcomes (e.g., with no water marks formed on hydrophobic substrates), matching the performance of Marangoni drying, with respect to absence of water marks and acceptable throughput, while avoiding the use of alcohol vapor.

[0010] In a further aspect, a meniscus of rinsing fluid may be formed on a substrate via a plurality of spray nozzles, rather than via immersion in a bath. For example, a rinsing fluid may be sprayed across the horizontal diameter of a vertically oriented substrate as it leaves a vertically oriented scrubber. An air knife may be applied at the meniscus or upper boundary of the rinsing fluid on the substrate, to thereby dry the substrate.

[0011] Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a schematic side view illustrating the inventive apparatus and method;

[0013]FIG. 2 is a flow chart that illustrates a method of operating the apparatus of FIG. 1; and

[0014]FIG. 3 is a schematic front elevational view of a scrubber that may employ an air knife.

DETAILED DESCRIPTION

[0015]FIG. 1 is a schematic side view of a vertical single wafer immersion drying apparatus 11 configured in accordance with the present invention. For example, the principles of the present invention may be applied to an immersion drying apparatus of the type disclosed in the above-referenced co-pending U.S. provisional patent application Serial No. 60/335,335, filed Nov. 2, 2001. The inventive immersion drying apparatus 11 includes a tank schematically represented at reference numeral 13. The tank 13 contains a fluid bath 15 constituted by a rinsing fluid 17 such as deionized water, a solution of a corrosion inhibitor such as BTA (benzotriazole) or the like.

[0016] A substrate 19 that is being dried in the inventive apparatus 11 is shown being raised in a substantially vertical orientation from the fluid bath 15. The substrate 19 may be, for example, a silicon wafer. A substrate raising mechanism schematically represented by an arrow 21 is provided to raise the substrate 19 from the fluid bath 15.

[0017] The substrate 19 has a front side 23 on which one or more material layers have been and/or will be formed. The substrate 19 also has a back side 25 that is opposed to the front side 23. During raising of the substrate 19, a first meniscus 27 of the fluid 17 is formed at an interface 29 between the front side 23 of the substrate 19 and a surface 31 of the fluid 17. A second meniscus 33 is also formed at an interface 35 between the back side 25 of the substrate 19 and the fluid surface 31.

[0018] In accordance with the invention, a first air-knife, schematically indicated by an arrow 37 a, is applied to the meniscus 27 at the front side 23 of the substrate 19. The first air-knife 37 a prevents the fluid 17 at the meniscus 27 from advancing upwardly with the front side 23 of the substrate 19 as the substrate 19 is raised, thereby drying the substrate 19. The first air-knife 37 a is applied at an angle 39 which is inclined downwardly from a horizontal plane 41. The angle 39 will be referred to as a “gas delivery angle”. The gas delivery angle may, for example, be in the range of 13°-30°, depending on the type of film formed on the substrate 19. Other gas delivery angles may be employed.

[0019] As shown, a second air-knife 37 b may be applied to the meniscus 33 at the back side 25 of the substrate 19, to aid in drying the back side 25 of the substrate 19. The back side gas delivery angle may, but need not, be different from the front side gas delivery angle. A different gas delivery angle may be preferred for the back side if the surfaces on the two sides have different characteristics. However, it is also contemplated to embody the immersion drying apparatus 11 with an air-knife only at the front side or back side of the substrate.

[0020] One advantage of the inventive immersion drying apparatus 11 including an air-knife applied to the fluid meniscus is that the same gas delivery angle 39 may be used in connection with drying both substrates having a hydrophilic film (e.g., TEOS) thereon and also with substrates having a hydrophobic film (e.g., a low k dielectric) thereon. In the absence of the air-knife 37 a, the meniscus 27 in the case of the substrate 19 having the hydrophilic film thereon would extend higher above the surface 31 of the fluid 17 than the meniscus formed with a substrate having a hydrophobic film thereon. However, the action of the air-knife 37 a shortens or deforms the meniscus formed on the hydrophilic film so that drying may occur at substantially the same point above the fluid surface 31 as in the case of a substrate having a hydrophobic film thereon.

[0021] In one embodiment of the invention, the air-knife 37 a (or 37 b) may be implemented by means of a nozzle (e.g., a spray tube; not separately shown) of the same type as the gas delivery spray tubes disclosed in the above-referenced co-pending provisional patent application Serial No. 60/335,335, filed Nov. 2, 2001. In addition, a suitable gas supply (not shown) is coupled to the nozzle. In one embodiment of the invention, the gas employed is nitrogen (N₂) although other gases may be used.

[0022] In a particular embodiment, a nozzle tube having a perforated length of about 8.5 inches (which may be used, for example, in drying a 200 millimeter wafer) and having 114 holes of 0.005-0.007 inches in diameter, uniformly distributed along the perforated length of the nozzle tube may be used. The holes preferably should all be colinear and have the same orientation. The nozzle tube may be formed of stainless steel, quartz, or another suitable material. Other configurations may be employed.

[0023] With such a nozzle tube, a gas flow rate of 15 liters per minute may be employed. Higher or lower gas flow rates could also be employed. For example, gas flow rates in the range of 10-30 liters/minute are specifically contemplated. In one embodiment, a gas delivery angle of 15° was found to be suitable for both hydrophilic and hydrophobic wafer surfaces. It is believed that this angle would also be appropriate for a patterned wafer surface having both hydrophilic and hydrophobic features. Further, it has been found that gas delivery angles in the range of 10°-20° may be preferred for drying a wafer having a hydrophilic film (TEOS).

[0024] In the same embodiment, the substrate 19 was raised while being inclined away from the front side air-knife nozzle tube at an angle of 9° from the vertical. The direction of motion of the substrate was in the inclined plane defined by the substrate, as in the immersion tank disclosed in the above-referenced co-pending provisional patent application Serial No. 60/335,335, filed Nov. 2, 2001.

[0025] The cross-sectional center of the nozzle tube was a distance of 0.36 inches above the fluid surface, and at a perpendicular distance from the fluid surface of 0.63 inches for the front-side nozzle. For the back-side nozzle, the perpendicular distance to the wafer was 0.51 inches. In this same embodiment, the speed of raising the substrate was 2.5 millimeters per second. However, satisfactory results have also been obtained with a speed of raising the substrate of 10 millimeters per second. There may be, in general, a trade off between substrate-raising speed and number of contaminants after the drying process, with higher substrate-raising speeds possibly resulting in a greater number of contaminants.

[0026]FIG. 2 is a flow chart that illustrates a method of operating the apparatus of FIG. 1. Initially, in step 51, the gas delivery angle is set (e.g., at 15°). The setting of the gas delivery angle may be performed, for example, by fixedly mounting an air knife 37 a and/or 37 b (e.g., one or more nozzle tubes) relative to the tank 13. Alternatively, each nozzle tube may be adjustably mounted relative to the tank 13 and may be manually or otherwise adjusted to set the gas delivery angle.

[0027] Next, at step 53, one or more hydrophobic substrates (i.e., substrates having a hydrophobic film on the front side thereof) are immersion-dried using an air-knife in accordance with the invention, with the gas delivery angle set at step 51.

[0028] Following step 53 is step 55, at which one or more hydrophilic substrates (i.e., substrates having a hydrophilic film on the front side thereof) are immersion-dried using an air-knife in accordance with the invention, with the gas delivery angle set at step 51.

[0029] It will be noted that the gas delivery angle is not changed between steps 53 and 55.

[0030] The order of steps 53 and 55 may be reversed, and again it is not necessary to change the gas delivery angle between the two steps.

[0031] The air-knife may be implemented using structure that is different from the nozzle tube described above. Gas flow rate may be varied and/or a gas other than nitrogen (N₂) may be employed.

[0032] The present invention may be applied to drying a substrate having a different size and/or a different shape than a 200 mm wafer (e.g., a square or rectangular glass substrate such as employed for flat panel displays). The length of the nozzle tube may be varied as appropriate.

[0033] The substrate may be raised at an angle other than 9° from the vertical, or may be raised without inclination (i.e., at 90° from the horizontal).

[0034] The air-knife/nozzle tube may be arranged so that the gas delivery angle is adjustable by, e.g., manual adjustment.

[0035] An alcohol vapor (e.g., isopropyl alcohol vapor) or another gas or vapor that serves to lower the surface tension of the rinsing fluid (i.e., a Marangoni drying gas) may be included in the gas dispensed by the air-knife nozzle tube (e.g., by the type of arrangement disclosed in the above-referenced co-pending provisional patent application Serial No. 60/335,335, filed Nov. 2, 2001) so that Marangoni effect drying is also employed in the inventive immersion drying apparatus. Alternatively, a separate Marangoni drying nozzle 43 a, 43 b (shown in phantom in FIG. 1) may be employed to supply Marangoni drying gas to a meniscus. The Marangoni drying nozzle 43 a, 43 b may be employed in addition to the air-knife 37 a, 37 b that manipulates the meniscus. By employing both an air-knife and a Marangoni drying gas, consecutive drying of hydrophilic and hydrophobic surfaces (or vice versa) may be employed without needing to adjust the position of the Marangoni drying nozzle 43 a, 43 b. Specifically, because the air-knife 37 a, 37 b manipulates the meniscus 27, 33 to the same position for both hydrophilic and hydrophobic surfaces, the Marangoni drying nozzle 43 a, 43 b may maintain the same position for drying of hydrophilic surfaces and hydrophobic surfaces. Accordingly, throughput may be increased and labor costs decreased.

[0036] Moreover, with use of the present invention (with or without application of a Marangoni drying gas) surfaces having both hydrophilic and hydrophobic portions (such as patterned semiconductor wafers) may be dried with better results (e.g., fewer contaminants).

[0037] In a further aspect, the invention may be employed within a vertically oriented scrubber. FIG. 3 is a schematic front elevational view of a vertically oriented scrubber 101, having a plurality of rollers 303 for supporting a substrate S. A front side and a back side scrubber brush 305 (only one shown) are positioned above the rollers 303 so as to contact the front and back sides of the substrate S positioned on the rollers 303. A fluid spray nozzle 307 is positioned above the scrubber brushes 305, and an air knife nozzle 309 is positioned above the fluid spray nozzle 307. An optional Marangoni drying nozzle 311 (shown in phantom) may be included. After the substrate S is scrubbed it may be dried via the air knife nozzle 309 (with or without the aid of a Marangoni drying vapor supplied either via the air knife nozzle 309 or via the Marangoni drying nozzle 311) in the manner described above with reference to FIGS. 1 and 2, as the substrate S is lifted from the rollers 303 (e.g., via a wafer handler or substrate pusher, not shown). Note that the rinsing fluid nozzle 307, the Marangoni drying nozzle 311 and the air knife nozzle 309 preferably are positioned above the upper perimeter of the substrate S when the substrate S is positioned on the rollers 303. In this manner the entire substrate surface is lifted past the nozzles 307-311. A second set of nozzles 307-311 may be similarly positioned along the back side of the substrate S.

[0038] The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, a substrate may be held at any orientation while being dried by an air knife. As stated, the present invention may be employed, for example, within a system similar to that described in previously incorporated U.S. Provisional Patent Application Serial No. 60/335,335, filed Nov. 2, 2001 (Attorney Docket No. 5877/L), entitled “Single Wafer Immersion Dryer and Drying Methods” or within any other suitable system.

[0039] Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims. 

The invention claimed is:
 1. A method of drying a substrate, comprising: raising the substrate out of a fluid bath; and during the raising step, applying an air-knife to a meniscus formed at an interface between the substrate and a surface of the bath.
 2. A method of drying a substrate, comprising: setting a gas delivery angle for an air knife used during an immersion-drying process; using the air knife during immersion drying of a hydrophilic substrate; and using the air knife during immersion drying of a hydrophobic substrate, wherein the gas delivery angle is unchanged during immersion drying of both the hydrophilic substrate and hydrophobic substrate. 